[Bug other/82857] libbacktrace: please support binaries stripped with dwz -m (following the .gnu_debugaltlink)

["vries at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82857

Tom de Vries <vries at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2018-11-01
                 CC|                            |vries at gcc dot gnu.org
     Ever confirmed|0                           |1

--- Comment #1 from Tom de Vries <vries at gcc dot gnu.org> ---
Test-case:
...
$ cat bt.c
#include "backtrace.h"

int
main (void)
{
  struct backtrace_state *state = backtrace_create_state ("./a.out", 0, NULL,
NULL);

  backtrace_print (state, 0, stderr);

  return 0;
}
...

Test script:
...
$ cat test.sh
#!/bin/sh

###########################

rm -Rf a.out ./a.out.debug

###########################

src=bt.c
pwd=$(pwd -P)

gcc_src=$pwd/src
gcc_build=$pwd/build

CFLAGS="-I $gcc_src/libbacktrace"
LDFLAGS="-lbacktrace -L $gcc_build/libbacktrace/.libs/"

gcc $src -O0 -g $CFLAGS $LDFLAGS

###########################

echo "Non-stripped"
./a.out 2>&1 | grep -c /bt.c

###########################

cp a.out a.out.debug
strip --only-keep-debug a.out.debug 
cp a.out.debug a.out.debug.saved

###########################

objcopy --strip-debug ./a.out
#strip a.out

echo "Stripped"
./a.out 2>&1  | grep -c /bt.c

###########################

objcopy --add-gnu-debuglink=a.out.debug ./a.out

echo "Stripped with debuglink"
./a.out 2>&1 | grep -c /bt.c

###########################

objcopy a.out.debug --compress-debug-sections=zlib

# We need to reset the debuglink, because the checksum has changed
objcopy -R .gnu_debuglink ./a.out
objcopy --add-gnu-debuglink=a.out.debug ./a.out

echo "Stripped with debuglink to compressed with objcopy"
./a.out 2>&1 | grep -c /bt.c

###########################

cp a.out.debug.saved a.out.debug

dwz a.out.debug

# We need to reset the debuglink, because the checksum has changed
objcopy -R .gnu_debuglink ./a.out
objcopy --add-gnu-debuglink=a.out.debug ./a.out

echo "Stripped with debuglink to compressed with dwz"
./a.out 2>&1 | grep -c /bt.c

###########################

cp a.out.debug.saved a.out.debug
cp a.out.debug.saved a.out.2.debug

dwz -m common.debug a.out.debug a.out.2.debug

# We need to reset the debuglink, because the checksum has changed
objcopy -R .gnu_debuglink ./a.out
objcopy --add-gnu-debuglink=a.out.debug ./a.out

echo "Stripped with debuglink to compressed with dwz -m"
./a.out 2>&1 | grep -c /bt.c
...

Test output:
...
$ ./test.sh
Non-stripped
1
Stripped
0
Stripped with debuglink
1
Stripped with debuglink to compressed with objcopy
1
Stripped with debuglink to compressed with dwz
1
Stripped with debuglink to compressed with dwz -m
0
...

Confirmed on master.